Most energy studies on the traditional ceramic manufacturing process focus on the firing stage because this is the process stage that consumes the greatest amount of thermal energy. At present in Europe, using typical technologies, about 50% of the energy input in the firing stage is still lost through the kiln stacks. A key issue in energy studies is the accurate determination of the energy efficiency of the process, an issue that may become crucial in coming years to enable the energy management of different facilities and products to be compared. To reliably determine energy efficiency, accurate determination is required of the energy needed for the necessary physico-chemical transformations to develop in the material in the firing stage. This energy is also the only strictly unrecoverable energy, as the energy contained in other streams could, potentially at least, be partly recoverable. The present study was undertaken to develop an analytical methodology for estimating the heat of reaction of seven different traditional ceramic products, involving a broad spectrum of compositions, with peak firing temperatures ranging from 850 ºC to 1200 ºC. The following industrial ceramic compositions were studied: four ceramic tile compositions (red-body stoneware tile, porcelain tile, red-body earthenware wall tile, and white-body earthenware wall tile); two structural ceramics compositions (white brick and roof tile), and a porcelain tableware composition. To estimate the energy involved in the physico-chemical reactions in the firing stage, an analytical methodology was developed, based on   the mineralogy data of the unfired body composition and on the enthalpy of formation of the minerals in the fired tiles. The methodology was validated by comparing the results with experimental data.

No abstract

This study examines the thermal decomposition process of the calcium carbonate (calcite powder) contained in test pieces of porous ceramics, of the same composition as that used in manufacturing ceramic wall tile bodies, in the presence of carbon dioxide, in the temperature range 1123 1223 K. The experiments were carried out in a tubular reactor, under isothermal conditions, in a gas stream comprising different concentrations of air and carbon dioxide.Assuming that the relationship between the molar concentrations of CO 2 on both sides of the gas solid interface in the test pieces was conditioned by an equilibrium law of the form The knowledge derived from this research has enabled the firing cycle used in the single-fire manufacture of this type of wall tile to be optimised. I ntroduction Object of this researchCalcite is the calcium compound that is usually added, as a source of CaO, to the raw materials mixture used to form the tile body in the single-fire manufacturing process of whitebody wall tiles 1 . During firing, the calcite particles need to completely decompose before the Corresponding author. e-mail address: aescardino@itc.uji.es 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 2 glaze melts and seals the tile surface in order to keep the CO 2 released in the tile body by this reaction from being trapped as small bubbles in the molten glaze layer 2 . *Manuscript Click here to view linked ReferencesIn order to optimise the calcite decomposition stage in the industrial firing cycle used to manufacture this type of tile, it was deemed useful to have a mathematical expression that would relate the decomposition progress of the calcite contained in the tile body to the operating variables (time, temperature, tile shape and size, etc.).The thermal decomposition process of very small calcite particles contained in ceramic compacts, analogous to those used in the manufacturing process to form white-firing earthenware tile bodies, has been studied in two previous papers 3,4 . The experiments were conducted in air atmosphere, at different temperatures, using disks of different initial porosity, thickness, and calcite content. The results were interpreted using an equation derived on applying the Shrinking Unreacted Core Kinetic Model.These papers have been the first phase of a study which has yielded a kinetic model that takes into account the influence of the dimensional and structural characteristics of the test disk and of the chemical reaction of decomposition that is developed. This kinetic model satisfactorily describes the kinetics of the process when is conducted in air atmosphere.In industrial practice, however, the thermal decomposition process of the calcite contained initially in the body of this type of tiles occurs in presence of a mixture of air and carbon dioxide that contains between 5 1...